This invention relates to an improved ballast circuit for an arc discharge lighting circuit and wherein improved current waveform to the lamp is provided, and particularly but not exclusively to ballasts for supplying power to arc discharge lamps such as for filming, commercial or street lighting. This invention also relates to the method of supplying a substantially square wave current derived from an alternating voltage source to feed an arc discharge lamp circuit.
An arc discharge lamp is a device for producing light output when electrical energy is applied to the connecting electrodes. In equipment used for driving arc lamps, it is well known that iron and copper reactors or electronic ballasts are used for regulating current to the lamp. The iron and copper ballast produces an approximate sine waveform current to the lamp and hence a modulated light output is obtained. Electronic ballasts produce either square wave or quasi sinusoidal current waveforms of varying frequencies, depending on the application, and often do not exhibit light modulation.
An advantage of electronic ballasts over conventional ballasts is that they often provide more power efficient operation of the lamp for a given power input. However, the high cost and lower reliability of electronic ballasts has limited application and usage.